I used RAW Photo Processor. Google and you will find it. Very limited. But free.

Couple quibbles.

Raw Photo Processor (a.k.a. "RPP") is an awesome tool. "Limited" in some senses — it's definitely not a DAM program, won't create a web site for you, etc. But as a raw converter it's fabulous — provided you're working on a Mac. (No Windows version.)

However, RPP is apparently NOT quite ready for the RX100. It will try to open the .ARW files, which I guess is something. But it doesn't handle blown/clipped exposure extremes at all well. I expect RPP will get around to this camera soon.

In the meantime, while I wait for Adobe, Apple and/or RPP to support the RX100, I'm shooting JPEG.